Universal Near-Field Interference Patterns of Fano Resonances in Two-Dimensional Plasmonic Crystals

We have demonstrated directly that the physical origin of Fano resonances in two-dimensional (2D) plasmonic crystals (PCs) is a wave-interference phenomenon. This is achieved by mapping the near-field interference patterns for low and high diffraction orders via three-dimensional finite element method (FEM) calculations. We show the near-field constructive and destructive resonances center at the corresponding Rayleigh anomaly (RA) wavelength of the lattice and lead to greatly enhanced and suppressed local electric fields around the nanoparticle, respectively. These collective resonances are generated by the coupling of localized surface plasmon resonances (LSPRs) with diffraction orders perpendicular or titled to the direction of the incident polarization, but not parallel to that. Further, it is revealed that such near-field interference patterns can apply to arbitrary 2D PCs. In addition, both the near- and far-field Fano-type spectral features are found to be continuously tuned by the lattice constants, which particularly benefit applications of PCs in enhanced sensing and emission.